04-Aug-2017, 22:31
After a first pass through it, I think Confused was right on the money (as usual). It's about an improvement to the ADH technology. In a nutshell, the idea is to reduce the stress on the class A amplifier, particularly at higher audio frequencies, so that it has to deliver less current and therefore is more accurate. This is done by adding a carefully designed loading network to the output of the class D amplifier.
Here's my attempt at translating the patent into something resembling normal English...with apologies for any misunderstandings on my part. (By the way I think there may be several typos that escaped the proof-reader, which threw me a little on first reading.)
Figure 1 shows the class A amplifier (in the box marked 18) and the class D amplifier (19). Their outputs are coupled to each other and the loudspeaker at point 14. This is the ADH core of all Devialet amplifiers. The class A amplifier is a very linear (accurate) voltage amplifier and the class D amplifier provides current to beef-up the output of the class A so it can drive real-world loads like loudspeakers. The class D amplifier inherently produces an on-off, pulse-width modulated (PWM) output which is merged with the class A's inherently analog output via an inductor (32A/B in the figure).
The class D amplifier is switching at a high frequency - effectively 2 MHz in Devialet's design - which is an engineering compromise between two opposing factors. First, at higher switching frequencies the class D amplifier is less efficient, i.e. generates more waste heat, because the transistors that implement the switches take a fixed time to turn on and off, during which they're dissipating lots of power (I x V). To make the class D as efficient as possible, then, you don't want it to switch at too high a frequency. On the other hand, at lower switching frequencies there is a higher ripple current through the inductor that couples the class D and class A amplifiers. The class A amplifier has to absorb that ripple current, which stresses it, causes it to dissipate more heat, and makes it less accurate.
Interestingly as a side note there is a hint (in paras 0016-0018) that operating the ADH system in a bridged, configuration is one way to reduce this ripple current and thereby allow the class A amplifier to be more accurate. Maybe that is a reason why the dual mono set up has a surprisingly large effect on sound quality, more than the increased power capability would suggest?
What the patent covers specifically is the addition of a damped RLC network (the components labelled 44x) that is carefully designed to reduce the ripple current at the class D switching frequency while having no noticeable effect at audio frequencies. This new network is presumably in the Pro amplifiers, while the original D-Premier and Expert series just have a resistor, according to para 0020.
As a result of this new RLC network, the class A amplifier has to "deal with" much lower ripple current from the class D, which makes it both more accurate and less power-hungry. I think this explains why Devialet said the Pro series sounded better because the current delivered by the class A amplifier was reduced relative to the class D.
Does that tally with anyone else's reading?
Here's my attempt at translating the patent into something resembling normal English...with apologies for any misunderstandings on my part. (By the way I think there may be several typos that escaped the proof-reader, which threw me a little on first reading.)
Figure 1 shows the class A amplifier (in the box marked 18) and the class D amplifier (19). Their outputs are coupled to each other and the loudspeaker at point 14. This is the ADH core of all Devialet amplifiers. The class A amplifier is a very linear (accurate) voltage amplifier and the class D amplifier provides current to beef-up the output of the class A so it can drive real-world loads like loudspeakers. The class D amplifier inherently produces an on-off, pulse-width modulated (PWM) output which is merged with the class A's inherently analog output via an inductor (32A/B in the figure).
The class D amplifier is switching at a high frequency - effectively 2 MHz in Devialet's design - which is an engineering compromise between two opposing factors. First, at higher switching frequencies the class D amplifier is less efficient, i.e. generates more waste heat, because the transistors that implement the switches take a fixed time to turn on and off, during which they're dissipating lots of power (I x V). To make the class D as efficient as possible, then, you don't want it to switch at too high a frequency. On the other hand, at lower switching frequencies there is a higher ripple current through the inductor that couples the class D and class A amplifiers. The class A amplifier has to absorb that ripple current, which stresses it, causes it to dissipate more heat, and makes it less accurate.
Interestingly as a side note there is a hint (in paras 0016-0018) that operating the ADH system in a bridged, configuration is one way to reduce this ripple current and thereby allow the class A amplifier to be more accurate. Maybe that is a reason why the dual mono set up has a surprisingly large effect on sound quality, more than the increased power capability would suggest?
What the patent covers specifically is the addition of a damped RLC network (the components labelled 44x) that is carefully designed to reduce the ripple current at the class D switching frequency while having no noticeable effect at audio frequencies. This new network is presumably in the Pro amplifiers, while the original D-Premier and Expert series just have a resistor, according to para 0020.
As a result of this new RLC network, the class A amplifier has to "deal with" much lower ripple current from the class D, which makes it both more accurate and less power-hungry. I think this explains why Devialet said the Pro series sounded better because the current delivered by the class A amplifier was reduced relative to the class D.
Does that tally with anyone else's reading?
Roon (Mac Mini), Wilson Benesch Full Circle, Expert 1000 Pro CI, Kaiser Chiara
Warwickshire, UK
